1. Field of the Invention
The present invention relates generally to a method for the production of animal milk having a high taurine content, and more particularly to a method for the production of natural taurine-enriched milk using biological metabolism, in which a precursor for synthesis of taurine is prepared in the as form of a pallet or matrix resistant to degradation in the rumen of ruminants and added to feedstuffs, such that biosynthesis of taurine is induced by stimulation of a substrate.
2. Description of the Prior Art
Taurine (2-amino-ethanesulfonic acid) is a sulfonic amino acid which is biologically synthesized in the body of mammals. This exists in a state free from intracellular fluids, and is found in skeletal muscles, such as cerebrum, eyeball, muscles, liver and the like, free amino acid groups and at high concentrations. Taurine has been used long in foods and drinks as a health additive having various functional characteristics, such as improvement of the liver function through detoxication and antioxidation actions, decreased blood cholesterol, and blood pressure adjustment. It was reported that taurine is combined with a bile acid in the body of predatory animals and is released through the bile in the form of taurocholic acid. In this case, taurine released into the bile has the effect of accelerating absorption of fat or fat-soluble vitamin in the intestine by a surface-active action. Also, it is effective in mitigating jaundice upon acute hepatitis by choleretic action, and in reducing blood neutral fat and cholesterol values in patients with hyperlipidemia. In addition, it was reported that taurine has a variety of functions, such as cerebral development, activation of photoreceptors of retina, reproduction, normal growth and development, antioxidant activity, and neural transmission, etc. (See, Jacobsen et al., Physiol. Rev. 48:424-511, 1968).
Because of such biological activities, taurine is used as an additive in various health foods or medical supplies, such as weaning diets for babies, gums, drinks, and nutritious tonic drinks, but is not practically used as drugs. Also, its reported therapeutic use was only for therapy of heart diseases.
In mammalian tissues, taurine is biologically synthesized from cysteine and methionine, that are sulfonic amino acids. In the case of the human body, however, the biological synthesis of taurine does not nearly occur, since activities of cysteine dioxygenase and cysteine decarboxylase involved in the biosynthesis of taurine is very low. As a result, the human body must be supplied with taurine externally (See, Vinton et al., Pediatr. Res. 21:399-403, 1987).
Meanwhile, taurine is maintained in mammalian tissues at high concentrations at nearly constant levels, but the taurine content in animal milk significantly varies depending on the kind of animal. According to results of the measurement of concentration of taurine in mature milk obtained from a variety of mammals (see, Rassin et al., Early Hum. Dev. 2(1):1-13; and Sarwar et al., British Journal of Nutrition 79:129-131, 1988), mature milks obtained from a zebra and a cat contain taurine levels of 595 xcexcmol/100 ml and 287 xcexcmol/100 ml, respectively, which are the highest concentrations among free amino acids contained in animal milk. Mother""s milk contains taurine of 34 xcexcmol/ml, which is next to glutamate in concentration. Meanwhile, mature milks from rats, rabbits and a sheep contain taurine of 14-15 xcexcmol/100 ml, while cow"" milk contains taurine of 1 xcexcmol/100 ml which is the lowest among the contents of taurine in milk of mammals. In particular, taurine in mother""s milk is a major amino acid, forming about 13% of the total free amino acids, whereas milk that is a main component of processed milk powder has the relatively low taurine content.
Because of such a low taurine content in milk, it was reported that a blood taurine level of immature infants and infants who ingest processed milk powder is reduced compared with infants who ingests mother""s milk (see, Rassin et al., Pediatrics 71:179-186, 1983; and Rigo et al., Biol. Neonates 32:73-76, 19970), although there was no clinical report of a taurine deficiency disease in adults who normally ingest meals. Also, the taurine reabsorption ability of babies is low due to the immaturity of renal tubules (Zelikovic et al., J. Pediatr. 116:301-306, 1990), while requirements for taurine is increased due to rapid growth of the body. As a result, for healthy growth and development, there is a need by babies for taurine. In particular, babies are significantly weak in synthesis, secretion and reuse of bile acids and have problems in digestion and absorption abilities of lipids. For this reason, emulsification of lipids will be insufficient, which is required to rapidly decompose the ingested lipids by pancreas lipase. Furthermore, as mother""s milk contains bile acid-stimulating lipase, it can efficiently decompose lipids with pancreas lipase even in an environment of low bile acid. However, processed milk for babies does not contain such a bile acid-stimulating lipase. Accordingly, in order to overcome the problems with processed milk powder, in the United States, taurine, which is effective in accelerating the absorption of fat or fat-soluble vitamins by a surface active action is added to processed milk powder so as to have the same taurine level as mother""s milk (Picone et al., Today July/Aug: 16-20, 1987). Moreover, the processed milk powder for infants now sold in Korea contains additionally enriched taurine.
Producing methods of taurine used for various applications includes a natural taurine-extracting method and a chemical synthesis method. The natural taurine-extracting method is a method of extracting a taurine component from mollusks, such as cuttlefish, octopus, shellfish and the like. However, although products obtained by the natural taurine-extracting method can be used in various applications including table use or medical use, they are small portion (about 1%) relative to all taurine products. Taurine products obtained by the chemical synthesis method are mainly used.
The chemical synthesis method includes a variety of methods. In the latter method, however, other impurities can be contained during the process of producing synthesized taurine and cannot be completely removed during the process of purifying the synthesized taurine. As a result, the synthesized taurine has limited use due to the remaining impurities. In particular, the inexpensive taurine cannot be used for table use.
Therefore, there is an increased need for natural taurine which can be used in various applications including table use and medical use. There was a method proposed which included recovering waste liquid including an exuvial and cooking fluid of a cuttlefish and producing a taurine-containing product (Korean Patent Laid-Open No. 00-58466). Also, a method of producing an egg containing taurine in a large amount was proposed, which comprised drying and powdering a wasted shell portion of a crab excluding the edible portion thereof and adding the resulting powder to animal feedstuffs (Korean Patent Publication No. 96-16856).
However, the above methods in which taurine is added directly to products, or the feedstuffs containing taurine in a large amount is supplied directly so as to produce products such as foods containing taurine in great quantities, have problems as described below. First, a problem with the methods in which taurine is added directly to products is that it reduces productivity since the amount of taurine supplied by the natural taurine-extracting methods described above is very low.
In addition, a problem with methods in which the feedstuffs containing taurine in great quantities are supplied directly is that, where it is applied to animals having rumen, the taurine is degraded by microbes present in the rumen so that it is difficult to produce products containing taurine at a desired level. Generally, a digestion process of nutrients in the ruminants having rumen is divided into a first step of fermentation by the microbes in the rumen, and a second step of digestion in the lower digestion organ. For this reason, nutrients which are effectively available in the ruminants, are formed by combining the total microbial nutrients synthesized in the rumen and nutrients transferred to the small intestine without degradation in the rumen. Meanwhile, the rumen microbes have strong proteolytic and deamination activities and thus rapidly decompose liquid proteins and amino acids, so that there are fears in which taurine contained in the animal feedstuffs, or a precursor amino acid for taurine synthesis, can be degraded in the rumen. Thus, many studies have been carried out to find methods of reducing the degree of degradation of proteins and amino acids in the rumen. As a result, methods, such as chemical treatment, utilization of amino acid analogue, encapsulation, esophageal groove closure, and selective operation of rumen metabolism pathway balance, etc. are used (Chalupa et al., J. Dairy Science 58(8):1198-1218, Chen et al., Analytical Chimica Acta 296:249-253, 1004).
Another problem with the method where taurine is added directly to the feedstuffs and fed to the animals, is that when an excess of taurine is present in vivo, rumen metabolism, and digestion and absorption after the rumination can be obstructed.
In order to solve the problems with the taurine supply according to the prior art and to produce milk having an increased content of taurine, the present inventors have prepared a precursor for taurine synthesis in a form resistant to degradation in the rumen and fed the prepared precursor to the animals, so that the taurine synthesis is induced in vivo, thereby producing a taurine-enriched milk. The precursor for taurine synthesis is sulfuric amino acids, such as cystein and methionine, that are necessary for animal protein metabolism and evaluated as first restriction amino acids, particularly for milk protein synthesis. Tissue, blood, urine and milk of the ruminants are low in taurine and cystein contents, in comparison with those of monogastric animals. This is caused by hereditary or physiological factors, and because all ruminants are grass-eating animals and the vegetable protein ingested by them is short of taurine and taurine sources. From this fact, where rumen degradation-protected methionine, which is not degraded and is absorbable in the small intestine, is additionally fed, there can be expected an increase in taurine content together with change in composition of milk protein by stimulation of a substrate. In other words, for the intestinal absorption of these amino acids involved in synthesis of taurine and secretion of taurine through milk, rumen bypass and protection of these amino acids from rumen degradation are important. For this, chemical treatment and encapsulation methods are expected to be effective.
There have been many studies conducted on pellets or methods of producing the same containing active ingredients, such as amino acids which are protected from degradation in the rumen of ruminants, as well as animal feedstuffs containing the pellets. However, these studies aim to improve the breeding method of ruminants through feeding of the active ingredients (Korean Patent Laid-Open No. 95-27379, Korean Patent No. 143766, U.S. Pat. No. 5,279,832, U.S. Pat. No. 4,181,708, and U.S. Pat. No. 5,776,483). There are no reports on the production of milk containing increased amounts of taurine, through feeding of the protected amino acids to the animals.
Therefore, the present invention is to provide a method of producing taurine-enriched milk using a biological metabolic pathway, in which pellet or matrix containing amino acids that are protected from degradation in the rumen of ruminants are added to animal feedstuffs, such that synthesis of taurine is induced by stimulation of a substrate.
It is a general object of the present invention to provide a production method increasing the content of taurine in milk, in which taurine is otherwise insufficient as in the case of general milk. Specifically, an object of the present invention is to overcome the problems with the direct supply of natural taurine according to the prior art in which taurine can be degraded in the rumen and obstruct the rumen metabolism or the digestive metabolism after rumination, and to provide a method of producing taurine-enriched milk by supplying taurine precursors resistant to the rumen degradation.
Furthermore, it is an object of the present invention to provide milk having a high content of taurine by the above method. Natural taurine-enriched milk of the present invention is enriched in taurine which is otherwise insufficient in general milk in comparison with mother""s milk. Thus, milk of the present invention is expected to be effective as functional milk beneficial to babies with high taurine requirements.
To achieve the objects as described above, the present invention provides a method of producing animal milk having a high taurine content, in which a precursor for taurine synthesis resistant to degradation in the rumen is prepared and fed to animals with concentrated foodstuffs, such that biosynthesis of taurine is induced by stimulation of a substrate.
In addition, the present invention provides milk which is increased in taurine content according to the above method of the present invention.
As used herein, the term xe2x80x9cmature milkxe2x80x9d means normal milk which is secreted after colostrum being secreted for 4 to 7 days after delivery of a milking cow and is constant in its components for about 300 days. The term xe2x80x9cprotected amino acidsxe2x80x9d means that precursor amino acids or derivatives thereof for biosynthesis of taurine are coated with additives including insoluble materials and fillers, such that they can be protected from degradation caused by enzymatic reaction of rumen microorganisms. A concrete example used in a preferred embodiment of the present invention is rumen protected DL-methionine (RP DL-Met) or rumen protected methionine hydroxy analogue (RP MHA). In addition, the term xe2x80x9crumen degradationxe2x80x9d means that soluble protein and amino acids are degraded due to the rumen pH, and proteolytic activity and deamination activity of rumen microorganisms.